This invention relates to the fusion bonding of thermoplastic articles, and more particularly to an apparatus and process employing platens having obliquely positioned surfaces to heat and fuse thermoplastic articles immediately prior to their joinder.
Fusion bonding, also known as heat sealing or hot plate welding, is frequently employed to form unitary manufactured parts from two or more constituent parts. The process involves heating the separate constituents, particularly along their bonding surfaces, then positioning them against one another with their respective bonding surfaces arranged in face-to-face relationship. The constituent parts are held together, usually under pressure, until the abutting surfaces solidify and the fusion bond is complete.
An apparatus particularly well adapted for fusion bonding of multiple elements is shown in U.S. Pat. No. 4,146,420 to Newkirk, granted Mar. 27, 1979, and assigned to the assignee herein. The apparatus includes two opposed rotatable workpiece carriers which transfer workpieces to be joined in rotary step-by-step motion, from a pair of loading stations to a heating station where surface portions are fused, and then to a bonding station where the individual fused surface portions are solidified and joined. A heating element is reciprocated with each incremental rotation of the workpiece carriers so as to permit the heating element surface to come into close proximity with the surfaces of the workpieces being bonded. As a consequence of undertaking multiple steps or operations simultaneously at different locations, the bonding of multiple parts is more rapid.
The presently disclosed apparatus is readily adapted to the high precision bonding of certain thermoplastic parts, including the bonding of parts consisting of foam thermoplastic parts such as expanded polystyrene or the like. The apparatus is also readily adapted to other applications where it is desired to reduce, diminish, or eliminate the seam between the previously individual or separate constituents. The present arrangement finds application whenever there is a requirement for more precise control over the temperature of individual constituents, particularly at their bonding surfaces, and a need to more precisely control the manner in which the heating platen or other heating member is withdrawn or removed from proximity with a constituent bonding surface immediately following the heating operation.
Therefore, it is an object of the present invention to provide an apparatus for the fusion bonding of thermoplastic articles which affords greater control over the temperature to which the surfaces of articles to be bonded are heated, particularly at or along their bonding surfaces and thus contributes to the production of more dimensionally accurate articles.
Another object of the present invention is to provide a process and apparatus for minimizing the time lapse between the fusion and bonding steps of a heat sealing cycle.
Another object is to provide a fusion bonding apparatus configured to reduce movement of convection cooling air currents at or around the bonding surfaces of thermoplastic articles about to be joined after fusion.
Yet another object is to provide an apparatus and method for bonding thermoplastic articles along an optimally smooth seam at the fusion region, thus reducing the size of any surface interruption at the fusion region through elimination of the creation of a noticably visible seam between the bonded articles, and further eliminating the need for separate bonding agents such as, for example, hot melt adhesives or the like.